Previously available doffers for spindle type cotton pickers include a stack of doffers, or pads, supported on a solid shaft. Some pads are in the shape of a flat disk with spacers inserted between each pad. The disks are sandwiched between the spacers, and a nut threaded on external threads at the end of the solid shaft tightly clamps the disks and spacer for rotation of the pads and spacers in unison with the solid shaft. Examples of such structures are illustrated in U.S. Pat. No. 4,819,415. Alternatively, the doffers may include integral axially extending hubs of cast aluminum in place of the separate spacers, such as shown in U.S. Pat. No. 5,014,502. If there is insufficient tensioning preload on the assembled doffer, the doffer can spin relative to the shaft. Once the pads begin to spin, the pads further loosen on the shaft, and the entire doffer column usually must be rebuilt.
The threaded stub shaft at the bottom of the doffer column receives a tensioning nut to provide the preload that sandwiches the doffers and spacers or hubs for rotation together with the doffer shaft. The small amount of mounting space at the lower end of the column usually requires a relatively thin nut with a minimal amount of thread engagement.
The doffer columns normally operate near the critical operating speed. If the doffer shaft is operated in an over-speed condition for even a short period of time, the shaft may bend. Therefore, increasing the critical operating speed of the doffer columns helps to eliminate shaft bending.